This invention relates to an electronic musical instrument, and more particularly to a music synthesizer type electronic instrument with a memory to store musical tone modulation control information and musical tone signal generation mode select information.
Generally known are music synthesizers that are provided with a voltage-controlled oscillator (VCO), a voltage-controlled filter (VCF), and a voltage-controlled amplifier (VCA). In a conventional music synthesizer, control waveforms generators are provided for producing musical tone signals rich in music expression. A control waveform generated by the control waveform generator and having a magnitude varying with time is coupled to each of VCF and VCA so that the frequency characteristic of VCF and the gain of VCA vary with time. In other words, the musical tone signal is modulated in its tone color and volume envelope. The control waveform may be coupled also to VCO so that the tone pitch of the musical tone signal may also vary with time. It is to be desired that the shape of the control waveform can be changed voluntarily by the player. Therefore, the control waveform generators are so designed that their control waveform parameters such as attack time, first decay time, sustain level, second decay time, etc. may be arbitrarily determined by parameter control analog signals externally applied thereto. The parameter control analog signals are provided by potentiometers connected across a power source and located in easy positions for the player to operate. During a performance, however, it is almost impossible for the player to change the shape of control waveforms by operating a plurality of potentiometers to change the modulation control mode for a musical tone signal being produced. Accordingly, a prior art synthesizer is provided with a multiplexer, analog-to-digital (A/D) converter, random access memory (RAM), digital-to-analog (D/A) converter, and the preset switches. The preset switches are adapted to select memory blocks in a RAM. In a storage mode, a set of parameter control analog signals are multiplexed in a time sharing manner in a regular sequence. The multiplexed analog signals are converted successively into digital signals by the A/D converter, and stored in a memory block of the RAM designated by an operated preset switch. In a read mode, a set of parameter control digital signals are read out successively from a memory block of the RAM corresponding to an operated preset switch, and converted successively into analog signals by the D/A converter. The time shared analog signals are then demultiplexed by a demultiplexer, and the demultiplexed analog signals are coupled to corresponding input terminals of a control waveform generator. According to such an electronic instrument, sets of control analog signals as many as the preset switches are stored in the RAM. Even during the performance, therefore, the player can voluntarily select the modulation control mode for a musical tone signal by only selecting a preset switch.
For improved music expression, besides increased faculties of modulation control of musical tone signals by control waveforms, a music synthesizer is required to have a function of selecting the generation modes of the tone signals. By such a generation mode select function, one of waveforms of a tone signal from VCO, for example, may optionally be selected, and a VCF may be set to any one of high-pass, band-pass, and low-pass filters. In the aforementioned prior art electronic musical instrument, generation mode select information is provided by a combination of on- and off-states of generation mode select switches, that is, by a multi-bit digital signal. A set of parameter control information signals and generation mode select information signals corresponding to one preset switch may be stored in a common RAM. Unlike the parameter control information signal, however, the generation mode select information signal is given in the form of a digital signal consisting of on-off combinations of the select switches, so that the analog multiplexer and demultiplexer for the parameter control information signals cannot be used for the generation mode select information signals. Thus, a digital multiplexer and a demultiplexer are additionally used for the generation of mode select information signals, requiring two signal processing systems and thereby complicating the construction of the instrument.